Semiconductor memory device and method of manufacturing the same

ABSTRACT

A semiconductor memory device comprises a plurality of transistors having a stacked-gate structure. Each transistor includes a semiconductor substrate, a gate insulator formed on the semiconductor substrate, a lower gate formed on the semiconductor substrate with the gate insulator interposed, an intergate insulator formed on the lower gate, and an upper gate formed and silicided on the lower gate with the intergate insulator interposed. A portion of the transistors has an aperture formed through the intergate insulator to connect the lower gate with the upper gate and further includes a block film composed of an insulator and formed smaller than the upper gate and larger than the aperture above the upper gate to cover the aperture.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority fromprior Japanese Patent Application No. 2007-260039, filed on Oct. 3,2007, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor memory device andmethod of manufacturing the same, and more particularly to a structureof a stacked-gate nonvolatile semiconductor memory and method ofmanufacturing the same.

2. Description of the Related Art

A NAND-type flash memory is well known as one of nonvolatilesemiconductor memories. Such the NAND-type flash memory comprises asemiconductor substrate on which memory cells and selection transistorsare formed together with peripheral circuits required for memoryoperation. A memory cell may include a floating gate composed ofconductive polysilicon formed on the semiconductor substrate with a gateinsulator interposed, and a control gate composed of conductivepolysilicon formed on the floating gate with an intergate insulatorinterposed.

On the other hand, the selection transistors and the transistors in theperipheral circuits are formed through process steps in accordance withformation of the memory cells. The transistors may include a lower gatecomposed of conductive polysilicon formed on the semiconductor substratewith the gate insulator interposed, and an upper gate composed ofconductive polysilicon formed thereon with an insulator interposed.

In this way, the NAND-type flash memory comprises a stacked-gatenonvolatile semiconductor memory having a plurality of gates stackedwith insulators interposed.

As for the selection transistors and the transistors in the peripheralcircuits, it is required to cause an electrical short circuit betweenthe upper gate and the lower gate in accordance with formation of memorycells such that they can serve as transistors. The electrical shortcircuit may be caused with an aperture formed through part of theintergate insulator between the upper gate and the lower gate.

If the transistor has a gate length of 50 nm or below on the other hand,the gate resistance increases and causes problems associated with lackof the voltage applied to the gate and the signal speed delay. Theseproblems may be solved by a full silicide structure including the entiregate silicided as proposed (see, for example, JP 2005-228868A).

Such the full silicide structure may be applied to the above-describedstacked-gate nonvolatile semiconductor memory. In this case, togetherwith fully siliciding the control gate, the upper gate of the selectiontransistor is also fully silicided. When the upper gate is fullysilicided, metal atoms can diffuse into the lower gate via the apertureformed through the insulator between the upper gate and the lower gate,thereby siliciding part of the lower gate electrode as well.

If the lower gate electrode is progressively silicided to the gateinsulator, the silicide contacts the gate insulator in some portions andthe conductive polysilicon touches the gate insulator in other portionsin mixture in the structure close to the gate insulator.

In that case, the operating characteristics of the transistor, such asthe threshold of the selection transistor, may vary and make itdifficult to keep stable transistor operation.

SUMMARY OF THE INVENTION

In an aspect the present invention provides a semiconductor memorydevice, comprising a plurality of transistors having a stacked-gatestructure, each transistor including; a semiconductor substrate, a gateinsulator formed on the semiconductor substrate, a lower gate formed onthe semiconductor substrate with the gate insulator interposed, anintergate insulator formed on the lower gate, and an upper gate formedand silicided on the lower gate with the intergate insulator interposed,a portion of the transistors having an aperture formed through theintergate insulator to connect the lower gate with the upper gate andfurther including a block film composed of an insulator and formedsmaller than the upper gate and larger than the aperture above the uppergate to cover the aperture.

In another aspect the present invention provides a semiconductor memorydevice, comprising: a plurality of memory cells, each including; asemiconductor substrate, a gate insulator formed on the semiconductorsubstrate, a lower gate serving as a floating gate formed on thesemiconductor substrate with the gate insulator interposed, an intergateinsulator formed on the lower gate, and an upper gate serving as acontrol gate formed and silicided on the lower gate with the intergateinsulator interposed; and a plurality of transistors formed togetherwith the memory cells, each transistor including; the semiconductorsubstrate, the gate insulator, the lower gate, the intergate insulator,and the upper gate, the transistor having an aperture formed through theintergate insulator to connect the lower gate with the upper gate andfurther including a block film composed of an insulator and formedsmaller than the upper gate and larger than the aperture above the uppergate to cover the aperture.

In another aspect the present invention provides a method ofmanufacturing a semiconductor memory device, comprising: forming a gateinsulator on a semiconductor substrate; forming a first conductive filmon the gate insulator; forming an intergate insulator on the firstconductive film; selectively forming an aperture by etching through theintergate insulator in part of a region for use in formation of atransistor; forming a second conductive film on the intergate insulator;forming a first insulator above the second conductive film; forming ablock film larger than the aperture to cover the aperture by selectivelyremoving part of the first insulator; forming a sidewall composed of asecond insulator on the sides of the block film and forming a gatepattern composed of the second insulator in a region for use information of control gates of memory cells; selectively removing thesecond conductive film, the intergate insulator and the first conductivefilm by etching with a mask of the block film, the sidewall and the gatepattern to form gates of the memory cell and the transistor; burying athird insulator around the formed gates; removing the second insulatorafter burying the third insulator; and siliciding the second conductivefilm by depositing a siliciding metal on an upper surface of a portionof the gates of the memory cell and the transistor from which the secondinsulator has been removed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a memory cell array in a NAND flash memoryaccording to an embodiment of the present invention.

FIG. 2 is a partly omitted view of an A-A′ line section of the NANDflash memory according to the embodiment of the present invention.

FIG. 3 is an illustrative view of a method of manufacturing the NANDflash memory according to the embodiment of the present invention.

FIG. 4 is an illustrative view of the method of manufacturing the NANDflash memory according to the embodiment of the present invention.

FIG. 5 is an illustrative view of the method of manufacturing the NANDflash memory according to the embodiment of the present invention.

FIG. 6 is an illustrative view of the method of manufacturing the NANDflash memory according to the embodiment of the present invention.

FIG. 7 is an illustrative view of the method of manufacturing the NANDflash memory according to the embodiment of the present invention.

FIG. 8 is an illustrative view of the method of manufacturing the NANDflash memory according to the embodiment of the present invention.

FIG. 9 is an illustrative view of the method of manufacturing the NANDflash memory according to the embodiment of the present invention.

FIG. 10 is an illustrative view of the method of manufacturing the NANDflash memory according to the embodiment of the present invention.

FIG. 11 is an illustrative view of the method of manufacturing the NANDflash memory according to the embodiment of the present invention.

FIG. 12 is an illustrative view of the method of manufacturing the NANDflash memory according to the embodiment of the present invention.

FIG. 13 is an illustrative view of the method of manufacturing the NANDflash memory according to the embodiment of the present invention.

FIG. 14 is an illustrative view of the method of manufacturing the NANDflash memory according to the embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS Embodiment of Device Structure

A semiconductor memory device according to an embodiment of the presentinvention will now be described with reference to the drawings.

FIG. 1 is a plan view of a cell area in a NAND flash memory according tothe embodiment of the present invention.

The cell area includes a plurality of bit lines BL (BL1, BL2, BL3, . . .) extending in the Y-direction in the figure formed therein. Formed in alower layer than these bit lines BL are a selection gate SGL and aplurality of word lines WL (WL1, WL2, . . . ) extending in theX-direction at right angles to the bit lines BL.

Each memory cells MC is formed below an intersection of the word line WLand the bit line BL and a plurality of such memory cells MC (MC1, MC2, .. . ) are serially connected along the bit line BL direction. Selectiontransistors ST are formed below an intersection of the selection gatesSGL and the bit line BL and connected to both ends of the seriallyconnected memory cells MC. These memory cells MC and the selectiontransistors ST are isolated from each other in the word line WLdirection by STI (Shallow Trench Isolation) extending along the bit lineBL direction.

FIG. 2 shows a partly omitted A-A′ line section of the NAND flash memorytaken along the bit line BL according to the embodiment of the presentinvention. The NAND flash memory according to the embodiment comprisesthe memory cell (MC) and the selection transistor (ST) operative toselect or control the memory cell.

A configuration of the memory cell (MC) is described first. The memorycell includes a P-type silicon substrate 11, and a floating gate 15 acomposed of conductive polysilicon doped with an impurity such asphosphorous (P) and formed on the silicon substrate 11 with a gateinsulator 14 a composed of silicon oxide interposed. In a memory celladjacent thereto in the word line (WL) direction (a gate widthdirection), the surface region of the silicon substrate 11, the gateinsulator 14 a and a lower portion of the floating gate 15 a areisolated from others by STI (not shown).

Deposited on the floating gate 15 a and the STI (not shown) is ahigh-permittivity intergate insulator 16 a composed of an ONO(SiO₂/SiN/SiO₂) film with a thickness of about 10 nm. Formed on theintergate insulator 16 a is a control gate 17 a, which is silicidedafter deposition of conductive polysilicon. The control gate 17 a has anentirely silicided full silicide structure as described later in detail.The control gate 17 a may be composed of a nickel silicide (NiSi), atungsten silicide (WSi), a cobalt silicide (CoSi) or a titanium silicide(TiSi), formed extending in the word line direction and shared by pluralmemory cells adjoining in the word line direction. Thus, the controlgate 17 a is stacked above the floating gate 15 a with the intergateinsulator 16 a interposed to configure a gate electrode 18 a having astacked structure.

The gate electrodes 18 a of memory cells adjoining in the bit line (BL)direction (a gate length direction) are isolated from each other by agate isolation layer 19 a composed of silicon oxide. In the presentembodiment, the line width of the gate electrode 18 a and the width ofthe gate isolation layer 19 a both along the bit line BL direction areformed such that the ratio therebetween, that is, a size ratio ofline-and-space becomes almost 1:1 preferably. The size ratio ofline-and-space is though not limited to 1:1.

Formed in the upper surface of the P-type silicon substrate 11 are anN-type source diffused region 12 a doped with an impurity such asphosphorous (P) and an N-type drain diffused region 12 a′ doped with animpurity such as phosphorous (P), which are formed sandwiching the gateelectrode 18 a there between in a self-aligned manner. The P-typesilicon substrate 11 may be a P-type well instead.

A configuration of the selection transistor (ST) is described next. Theselection transistor (ST) includes the P-type silicon substrate 11, anda lower gate 15 b composed of conductive polysilicon doped with animpurity such as phosphorous (P) and formed on the P-type siliconsubstrate 11 with a gate insulator 14 b composed of silicon oxideinterposed. In a selection transistor adjacent thereto in the word line(WL) direction, the surface region of the silicon substrate 11, the gateinsulator 15 a and a lower portion of the lower gate 15 b are isolatedfrom others by STI (not shown).

Deposited on the lower gate 15 b is a high-permittivity intergateinsulator 16 b composed of an ONO (SiO₂/SiN/SiO₂) film with a thicknessof about 10 nm. Formed through the intergate insulator 16 b almost atthe central portion in the bit line (BL) direction on the upper surfaceof the lower gate 15 b is an aperture 13. Formed on the intergateinsulator 16 b is an upper gate 17 b, which is silicided afterdeposition of conductive polysilicon. The upper gate 17 b has fullsilicide portions which are fully silicided in a film thickness range atleast at both ends in the bit line BL direction. The upper gate 17 b maybe composed of a nickel silicide (NiSi), a tungsten silicide (WSi), acobalt silicide (CoSi) or a titanium silicide (TiSi) formed extending inthe word line direction and shared by plural selection transistorsadjoining in the word line direction. Thus, the upper gate 17 b isstacked above the lower gate 15 b with the intergate insulator 16 binterposed to configure a gate electrode 18 b having a stackedstructure.

The upper gate 17 b is electrically connected to the lower gate 15 b viathe above-described aperture 13. A block film 20 composed of siliconoxide is formed on the upper gate 17 b. The block film 20 is larger thanthe aperture 13 to cover the entire of the aperture 13 and smaller thanthe upper gate electrode 17 b as shown in FIG. 1. The block film 20 isarranged to prevent metal atoms from diffusing into the inside of thelower gate 15 b through the aperture 13 when the upper gate 17 b isfully silicided and reaching the gate insulator 14 b.

The function of the block film 20 is described in more detail. Thecontrol gate 17 a and the upper gate 17 b can be fully silicided bydepositing a film of a metal such as Ni through a process of sputtering,followed by annealing to diffuse metal atoms. Unless the block film 20is present when Ni is sputtered into the surface of the upper gate 17 b,Ni atoms deposit over the entire surface of the upper gate 17 b.Usually, in full siliciding, Ni atoms are sputtered excessively inconsideration of variations in reaction. In this case, Ni atoms diffuseinto the lower gate 15 b through the aperture 13, and finally into thegate insulator 14 b, after the upper gate 17 b is fully silicided. Thisresults in variations in the characteristics of transistors anddeteriorates the reliability of memory elements.

The present embodiment provides the block film 20 on the surface of theupper gate 17 b to solve the above problem. When Ni is sputtered intothe surface of the upper gate 17 b, Ni atoms are blocked by the blockfilm 20 and allowed to deposit only on portions other than the portionimmediately beneath the block film 20. The other portions contain gaps21, 22 between the block film 20 and a gate isolation layer 19 b forisolating the gate electrode 18 a of the memory cell from the gateelectrode 18 b of the selection transistor. Ni atoms deposited on theportions containing the gaps 21, 22 diffuse into the inside of the uppergate 17 b and silicide the upper gate 17 b. The distance from the gaps21, 22 to the aperture 13 is longer than the distance from the gaps 21,22 to the intergate insulator 16 b. Therefore, a region 23 almostimmediately above the aperture 13 progresses the silicide reactionslower than in other regions. As a result, Ni atoms can be suppressed todiffuse into the lower gate 15 b through the aperture 13 and preventedfrom reaching the gate insulator 14 b.

The width of the block film 20 and the width of the aperture 13 can bedesigned freely. In order to ensure the contact resistance of the uppergate 17 b with the lower gate 15 b sufficiently, it is not preferable tomake the size of the aperture 13 too small. The size of the block film20 can be adjusted to confine the siliciding metal atoms deposited onthe upper surface of the upper gate 17 b to the area set by the gaps 21,22.

Formed in the upper surface of the P-type silicon substrate 11 are anN-type source diffused region 12 b doped with an impurity such asphosphorous (P) and an N-type drain diffused region 12 b′ doped with animpurity such as phosphorous (P), which are formed in a self-alignedmanner sandwiching the gate electrode 18 b therebetween. The P-typesilicon substrate 11 may be a P-type well instead. A channel region isformed immediately beneath the gate insulator 14 b between the N-typesource diffused region 12 b and the N-type drain diffused region 12 b′.

In the NAND flash memory according to the present embodiment, afterfully siliciding the control gate 17 a and the upper gate 17 b,siliciding of the lower gate 15 b through the aperture 13 can beprevented from excessively progressing to allow metal atoms to diffuseinto the gate insulator 14 b. As a result, it is possible to provide aNAND flash memory with high reliability.

In the above embodiment the configuration of the selection transistor isdescribed though transistors Tr in peripheral circuits can be configuredsimilarly.

[Embodiment of Manufacturing Method]

An embodiment associated with a method of manufacturing theabove-described NAND flash memory is described in detail with referenceto the drawings. FIGS. 3-14 illustrate process steps of manufacturingthe NAND flash memory according to the above-described embodiment.

In step 1, the surface of the semiconductor substrate 11 such as asilicon substrate is subjected to thermal oxidation to form the gateinsulator 14 composed of silicon oxide with a film thickness of 10 nm asshown in FIG. 3. Then, a process of CVD is applied to deposit a firstconductive polysilicon film 15 doped with phosphorous (P) at a certainconcentration with a thickness of 10 nm. Although not shown in thefigure, STI is used to separate the first polysilicon film 15, the gateinsulator 14 and the surface region of the semiconductor substrate 11into portions in the word line direction.

Then, a process of CVD is applied to deposit the intergate insulator 16such as an ONO (SiO₂/SiN/SiO₂) film. Subsequently, the aperture 13 forshort-circuiting between the upper gate 17 b and the lower gate 15 b ofthe transistor is patterned and formed in part of the region for use information of the selection transistor (ST) (this is similarly applied tothe transistors in peripheral circuits).

Thereafter, processes of CVD are applied to sequentially deposit apolysilicon film 17 with a thickness of 100 nm, a silicon oxide film 50such as a TEOS film with a thickness of 150 nm, and an antireflectivefilm 51.

Subsequently, a spin coating method is used to apply a photoresist overthe entire surface, followed by pattering through a photolithographytechnology to selectively form masks 62 a, 62 b, 52 b. The masks 62 a,62 b in the memory cell area differ in line pattern from the mask 52 bin the selection transistor area. Namely, the memory cell area includesa line pattern formed with a smaller width than the selection transistorarea. The line pattern and the space pattern in the memory cell areahave a ratio of almost 1:3. Such the pattern may be formed to have theratio of almost 1:3 by slimming of the pattern, after forming the linepattern and the space pattern having a ratio of almost 1:1 in the memorycell area.

In step 2, an anisotropic etching such as RIE is applied to selectivelyremove the antireflective film 51 and the silicon oxide film 50. Then,ashing and wet etching are applied to remove the masks 62 a, 62 b, 52 band the antireflective film 51 to form hard masks 63 a, 63 b, 53 b asshown in FIG. 4.

In step 3, a process of plasma CVD is applied to deposit a siliconnitride 54 over the entire surface as shown in FIG. 5. The filmthickness of the deposited silicon nitride 54 is set almost equal to theline size of the patterned hard masks 63 a, 63 b.

In step 4, a dry etching such as RIE is applied to etch back the siliconnitride 54 to form sidewalls 64 a, 64 a′, 64 b, 64 b′, 54 b, 54 b′ onthe sides of the hard masks 63 a, 63 b, 53 b as shown in FIG. 6. Thelateral thickness of the sidewalls 64 a, 64 a′, 64 b, 64 b′, 54 b, 54 b′becomes almost equal to the line width of the hard masks 63 a, 63 b. Thelateral thickness of the sidewalls 64 a, 64 a′, 64 b, 64 b′, 54 b, 54 b′can be controlled by the film thickness of the deposited silicon nitride54.

In step 5, a resist is applied over the entire surface and aphotolithography technology is used to form a mask 55 for covering theregion for use in formation of the transistor as shown in FIG. 7.

In step 6, a wet etching with DHF (dilute hydrofluoric acid) is appliedto remove the hardmasks 63 a, 63 b from the memory cell area as shown inFIG. 8. Then, ashing and wet etching are applied to remove the mask 55.The remaining sidewalls 64 a, 64 a′, 64 b, 64 b′ are used to form gatepatterns at a smaller pattern pitch than the pattern pitch of the linepatterns in the hard masks 63 a, 63 b. In this case, the line pattern(gate pattern) and the space pattern have a ratio of about 1:1.

In step 7, the hard mask 53 b and the sidewalls 64 a, 64 a′, 64 b, 64b′, 54 b, 54 b′ are used as an etching mask for anisotropic etching suchas RIE to form the gate electrode 18 a of the memory cell and the gateelectrode 18 b of the selection transistor as shown in FIG. 9.

In step 8, ions of phosphorous (P) are implanted at a concentration of1×10¹⁸ cm⁻³ to form N-type source regions 12 a, 12 b and N-type drainregions 12 a′ and 12 b′ as shown in FIG. 10. In this case, the sidewalls64 a, 64 a′, 64 b, 64 b′, 54 b, 54 b′ serve as masks together with thehard mask 53 b to form respective diffused regions in a self-alignedmanner.

In step 9, a process of plasma CVD is applied to deposit an interlayerinsulator such as a TEOS film over the entire surface, which is buriedbetween the gate electrode 18 a and the gate electrode 18 b as shown inFIG. 11. Then, a process of CMP is applied to planarize the surface toform the gate isolation layer portions 19 a, 19 b. In this case, thesidewalls 64 a, 64 a′, 64 b, 64 b′, 54 b, 54 b′ serve as stopper films.The gate isolation layer portion 19 a electrically separates the gateelectrodes 18 a of the memory cells from each other. The gate isolationlayer portion 19 b electrically separates the gate electrode 18 a of thememory cell from the gate electrode 18 b of the selection transistor.

In step 10, a process of RIE with CH₃F gas or a wet etching withphosphoric acid is applied to remove the sidewalls 64 a, 64 a′, 64 b, 64b′, 54 b, 54 b′ as shown in FIG. 12, thus forming the block film 20.

In step 11, a sputtering method is used to deposit atoms 55 of a metalsuch as Ni over the entire surface as shown in FIG. 13.

Finally, in step 12, an annealing process is applied to react Ni withpolysilicon in the control gate 17 a and the upper gate 17 b to formnickel silicide, thereby fully siliciding the control gate 17 a and theupper gate 17 b as shown in FIG. 14. The method of siliciding is notlimited to this example.

In full siliciding, the block film 20 formed on the surface of the uppergate 17 b blocks the deposition of Ni atoms on the surface at the centerof the upper gate 17 b. Therefore, Ni atoms are allowed to deposit onlyon the portions in the gaps 21, 22 between the block film 20 and thegate isolation layer portion 19 b. Ni atoms diffused into the upper gate17 b by annealing take a longer time to reach near the aperture 13 thanother regions because the distance to the aperture 13 is longer. As aresult, Ni atoms can be prevented from diffusing into the inside of thelower gate 15 b through the aperture 13.

In accordance with the method of manufacturing semiconductor memorydevices according to the present embodiment, metal atoms can beprevented from diffusing into the gate insulator even if the upper gateof the transistor is fully silicided. As a result, it is possible toensure stable operation of transistors.

In accordance with the method of manufacturing semiconductor memorydevices according to the present embodiment, the sidewalls 64 a, 64 a′,64 b, 64 b′ are formed on both sides of the hard masks 63 a, 63 b toform memory cells MC with a mask of the sidewalls. Accordingly, finepatterning beyond the exposure resolution limit for hardmask formationcan be achieved easily and thus can realize high integration.

[Others]

The embodiments of the invention have been described above though thepresent invention is not limited to these embodiments but rather can begiven various modifications and additions without departing from thescope and spirit of the invention. For example, the NAND flash memory isdescribed in the above embodiments though the present invention is alsoapplicable to other stacked-gate nonvolatile memories such as a NORflash memory.

1. A semiconductor memory device, comprising a plurality of transistorshaving a stacked-gate structure, each transistor including; asemiconductor substrate, a gate insulator formed on said semiconductorsubstrate, a lower gate formed on said semiconductor substrate with saidgate insulator interposed, an intergate insulator formed on said lowergate, and an upper gate formed and silicided on said lower gate withsaid intergate insulator interposed, a portion of said transistorshaving an aperture formed through said intergate insulator to connectsaid lower gate with said upper gate and further including a block filmcomposed of an insulator and formed smaller than said upper gate andlarger than said aperture above said upper gate to cover said aperture.2. The semiconductor memory device according to claim 1, wherein atleast a portion of said upper gate is fully silicided in a filmthickness range.
 3. The semiconductor memory device according to claim1, wherein metal atoms in said silicided upper gate of said transistorare not diffused into said gate insulator through said aperture.
 4. Thesemiconductor memory device according to claim 1, wherein said apertureis formed almost at the center of the upper surface of said lower gate.5. The semiconductor memory device according to claim 1, wherein saidupper gate is composed of a nickel silicide, a tungsten silicide, acobalt silicide or a titanium silicide.
 6. A semiconductor memorydevice, comprising: a plurality of memory cells, each including; asemiconductor substrate, a gate insulator formed on said semiconductorsubstrate, a lower gate serving as a floating gate formed on saidsemiconductor substrate with said gate insulator interposed, anintergate insulator formed on said lower gate, and an upper gate servingas a control gate formed and silicided on said lower gate with saidintergate insulator interposed; and a plurality of transistors formedtogether with said memory cells, each transistor including; saidsemiconductor substrate, said gate insulator, said lower gate, saidintergate insulator, and said upper gate, said transistor having anaperture formed through said intergate insulator to connect said lowergate with said upper gate and further including a block film composed ofan insulator and formed smaller than said upper gate and larger thansaid aperture above said upper gate to cover said aperture.
 7. Thesemiconductor memory device according to claim 6, wherein at least aportion of said upper gate is fully silicided in a film thickness range.8. The semiconductor memory device according to claim 6, wherein metalatoms in said silicided upper gate of said transistor are not diffusedinto said gate insulator through said aperture.
 9. The semiconductormemory device according to claim 6, further comprising a gate isolationlayer arranged to isolate said upper and lower gates between memorycells adjoining in a gate length direction, wherein said upper and lowergates and said gate isolation layer are formed in a measurement ratio ofalmost 1:1 in said gate length direction.
 10. The semiconductor memorydevice according to claim 6, wherein said upper gate of each of saidmemory cells is formed extending in a gate width direction and shared bysaid memory cells adjoining in said gate width direction.
 11. Thesemiconductor memory device according to claim 6, wherein said uppergate of said transistor is formed extending in a gate width directionand shared by said transistors adjoining in said gate width direction.12. The semiconductor memory device according to claim 6, wherein saidaperture is formed almost at the center of the upper surface of saidlower gate.
 13. The semiconductor memory device according to claim 6,wherein said upper gate is composed of a nickel silicide, a tungstensilicide, a cobalt silicide or a titanium silicide.
 14. Thesemiconductor memory device according to claim 6, wherein said memorycells are connected in series, of which both ends are connected to saidtransistors to configure a NAND-type flash memory.
 15. A method ofmanufacturing a semiconductor memory device, comprising: forming a gateinsulator on a semiconductor substrate; forming a first conductive filmon said gate insulator; forming an intergate insulator on said firstconductive film; selectively forming an aperture by etching through saidintergate insulator in part of a region for use in formation of atransistor; forming a second conductive film on said intergateinsulator; forming a first insulator above said second conductive film;forming a block film larger than said aperture to cover said aperture byselectively removing part of said first insulator; forming a sidewallcomposed of a second insulator on the sides of said block film andforming a gate pattern composed of said second insulator in a region foruse in formation of control gates of memory cells; selectively removingsaid second conductive film, said intergate insulator and said firstconductive film by etching with a mask of said block film, said sidewalland said gate pattern to form gates of said memory cell and saidtransistor; burying a third insulator around said formed gates; removingsaid second insulator after burying said third insulator; and silicidingsaid second conductive film by depositing a siliciding metal on an uppersurface of a portion of the gates of said memory cell and saidtransistor from which said second insulator has been removed.
 16. Themethod of manufacturing a semiconductor memory device according to claim15, further comprising forming a line pattern composed of said firstinsulator at a position between gates of said memory cells together withthe step of forming a block film, wherein forming a sidewall and a gatepattern includes depositing said second insulator on said block film andsaid line pattern, then etching back said deposited second insulator,and selectively removing said first insulator from a region for use information of said memory cells, thereby forming said gate pattern havinga smaller pattern pitch than the pattern pitch of said line pattern ofsaid first insulator.
 17. The method of manufacturing a semiconductormemory device according to claim 16, wherein forming a line patternincludes forming said line pattern with a ratio of about 1:3 betweensaid line pattern and a space pattern between said line patterns, andforming a gate pattern includes forming said gate pattern on the sidewall of said line pattern with a ratio of about 1:1 between said gatepattern measurement and said line pattern measurement.
 18. The method ofmanufacturing a semiconductor memory device according to claim 15,wherein said siliciding metal is nickel, tungsten, cobalt or titanium.19. The method of manufacturing a semiconductor memory device accordingto claim 15, wherein siliciding said second conductive film includessiliciding entirely said second conductive film of said memory cells.20. The method of manufacturing a semiconductor memory device accordingto claim 15, wherein said first insulator is silicon oxide and saidsecond insulator is silicon nitride.